strange effects with lights..plus sill advise needed

hello all...i have a diesel escort 55 van on a s plate..problems are..failed mot..due too sill needing renewal ,anyone know as too the cost and more specific where i buy them cheaply..and cost of this welding..also more important..maybe this is easy..rear brake lights on this van are of the twist on type.with no wiring protruding as the cluster body is the live and earth source i think.well the units what hold the bulbs have signs of severe burning(not the cluster body but the holder itself..heat proof outter on it? three nibbs hold it onto the cluster unit? clear?ok kool lol.)..but where do i but them from..and would this carbon build up be the cause of why my dippedheadlights light up glowing when i push down the brake,how could these two problems be related ?..and if on the same loom would this occour at the front when pressing the brake...im completly miffed :(